Magnetron filament temperature regulator



June 15, 1948. K. JENKINS 2,443,139

MAGNETRQN FILAMENT TEMPERATURE REGULATOR Filed Feb. 7, 1946 Patented June 15, 1943 MAGN ETRDN FILAMENTMTEMPERATURE REGULATOR Kenneth'DQJenkins, Oakland, Calif'. Application; Febmary-;:7, 1946, Serial No.,64 6,'1 88,e 8 Claims. (o1. sis -me t The inventionwlescribed herein may: be-manufactured'and used by o-r fo'r the Government-- f or': governmental purposes without payment to i me of any royalty thereon.

This invention-relates to vacuuintube apparatus and particularly --pertains to the regulation of magnetron filament temperatures.

In -certain applications, the plate voltage-of magnetrontubes must be interrupted frequently in which case it becomes necessaryto lower the filament voltage each time plate voltage is "applied due tothe backheating which is caused by bombardment of electrons that do not go to'the plate-but return tothe; filament and-bombard the latter with sufiicient-force' to causeexcessive-- heatingthereof. Consequently,- it is particularlydesirabletoprovide a means for the automatic" regulation of 'filament voltage so as to insure a constant filament temperature.

It is an object of this invention,therefore;--toprovide a method of controlling the operating filament temperature of vacuum tubes--by- -utilizing the variation in the ratio of filament current to "filament voltage produced by changes in'filament- 'temperaturei It is a i-urther object of this invention to provide a. method of controlling .the operatingfila menttemperature of vacuumtubes; by detecting:

and measuring the-variation inthevratiov of- -fila-ait ment currenttofilament voltage; and uti1izing:=-

such measured'variation to control thefilament temperature by readjustment of the filament voltage.

A -further' object of this :invent-ion is tOnprO vide means -:for automatica1ly regulatingithe' NoltL-jz tain the'filament: at a constant temperature.

As still further object of this-invention is :to-

provide ameans fordetecting variations =in 'fila-A ment current .with" respect to filament-voltage andfor; utilizing these variations to control the voltage I drop across the filament.

Other objects and featuresn-of this. invention will become apparent when the iollowingrldescriprtion isreadiin' connection Withithe lannexededraw-h main which is shown a schematic ldiagram ofia' preferred embodimentaof my inventiom According to my invention generally, nit-.- is pro-g posed to -.connect,'- in series with: at. magnetronu;

filament transformer; a. variable (saturahlelerea.

actor whose secondary" winding l: mayw hes-cone v trollec'l hy: a -means responsive to filament: n:: the :-.filament transformer :wh'en hackheatingaoc:

rent. i'fiuctuations; sov as: to i. reduce: the, 1 voltage r curs:-

21.1, lnithegdrawing the primary winding .9 of the; filamentzh'transzformer I ii :is, ;oo.nnected in -..serie.s. withsthe A;lCcwi'ndings:.-! l 60f, a :va-riable reactor l2 iand'ta fixedresistor;l3,;'across an .A. Cirxpoweri The frequency-;-ofvthe;A. 10.: power source.

may be between 400 and 1600 ,cyclesimthe; case 1 o'fxairora-ft:syste ns;,;or- 60., cycles. in: ground in:

stailation The filament transiormersecondary winding:t'eisieonnected to the filament l 6 of mag-- -netr.Qn The voltage drop appearingzacross A. V

C.; Winding; I I; i: will vary; depen ding ;upon ,the amountzzeof. current flow-ingeuthrough: the ..D ;C. winding] 8 oft-"the :saturable: reactor; I 2 The volt:

aee;a.dr,op;;aor,oss .the:filamentmransformer prim marmwindinafi will vary inverselyiwithythe;.vo1tagezidrepggaoross; windingd l, provided-50f;- courses, resistor 13- i.-;relatively:;1ow-resistance;

= imentecurrenty. afterrbeing Uappliedato a I halar 1;=c.d v

detector circuit, operates to control the bias-yofi a ,.vacuumigtube-@Whose output-,; current; flows through- :the LB-.10, (cont-r01) iwindineeof the :variableiireactolzt-x Since the resistanceor a tungstenfilament; varies; dire ctly witht-the.ztemperature :rise of the filamentqover the: operating range, ,then item-1 pe-rature; chan es can: beedeterminede ytm a r urine wand: comparing the voltagev ;:-and current, "required!to-iheat-rthe filament The secondary of;;

a f lamentqtrans-f-ormersis 31151131113 at ahigh negative- Dr ;C-.. potential,- andit. isi-therefore more-i practical-t0 imcasurerthe current ,andvoltage {in 1 the ;primary 5 since tha voltage and. current in: i the primaryg pfqa Ltransiormer: is directly pro-e portional to -the gvoltage 'and currentdn:the sec-1 nclary -i According-1 m me ,invention, la transformer I 9 fon emeasuringgvoltage his connec-ted ..in parallel to withntha; magnetron; filament -.transformer. A

transformer-'20 for measuring current imaye be connected; either: inn: series with the, filament, transformer; on, it tmaya bei'connected across- :an resistor-gwhich is, in Q series with the, filaments transformer 'T hetlatterarrangement -is ,shown in g the draw-ing and; is- :consideredlto be the more desirable arrangement for-the (followin reason-:1, Wham measuring ;,current,-:through a circuit, .it; is customary to'use :a-transformer having a fe,w:----

-turns-,on- ,the primary andcmany turns on the,

secondar l provideda constant frequency poyven l source is. lusedat Hpwov ri a e thelsecondaryi volta er of a transformer is -a rfunction of lire-rs q ncy as .we11t as; the c rrent, in ;-the :primar-Yi I when a: variahle frequency power: source (is used,:-

eeexplained how a ;,differventia1. .1

it becomes preferable to use a low resistance in series with the primary of the magnetron filament transformer, and to measure the voltage drop across the resistor. Such a resistor, however, in addition to having a flat frequency response, should have asubstantially zero temperature coefilcient since varying currents v through the resistor would otherwise cause its resistance to vary.

Experiment has shown that peak values of magnetron filament current and voltage do not vary uniformly because of harmonic distortion and leakage inductance in reactor 12. other hand, it has also been found that the actual R. M. S. values of voltage-and current do vary uniformly. Therefore, it is desiralzile to measure the R. M. S. value of voltage and current or preferably to use average readin detectors, since the average values of voltage and current ,are more easily measured and closely follow M. S. values. Average reading detectors have proportionately lower voltage outputs than'have peak reading detectors, consequentlysome amplification of the control voltage is usually necessary in order to meet control range requirements.

Referring again to the drawing, the secondary. windings of transformers I9 and 28 are connected Y to the plates of diodes 2| and 22 respectively. Two resistors 23 and 24 of equal size are connected across the cathodes of diodes 2| and22 respectively, and the midpoint of said resistors is tied to a connection between the secondaries of transformers l9 and'28 as shown. In operation, D. C. output voltages will exist across resistors 23 On the across resistor 29. The negative bias thus cre-' and 24, which follow-variations in magnetron filament voltage and current respectively. The algebraic sum of the voltages across resistors 23 and 24 will produce a reference voltage which will be the difference between'the two D. C. output voltages.

A variable resistor 25-is inserted in the output from tube 2| simply for the purpose of adjusting the relative outputs from the two diodes during initial setting of the filament-voltage. I

Resistor 28 in conjunction with condenser 21 forms a filter section'for deriving an average filtered reference voltage which can be applied to the'grid oftube 28. The cathodes of tube 28 and diode 22 are connected together and to ground. Tube 28 serves to amplify the reference voltage. 'A plate load resistor 29 connecting the 'plate of tube. 28 to the cathode of amplifying tube 38 is supplied with a low positive D. C. volt-' age 35. The plate of tube 28 is directly coupled to the grid of tube 38; The D. C. 'plate voltage to tube 38 is supplied from a source of positive D. C. voltage 34 through a series circuit comprising the reactor winding I 8 and the operating coil 3| of a relay 32. This relay interrupts the voltage to the magnetron anode 33 when the filament sistance increases, lowering the filament current,

causing a lower voltage drop across resistor l3 and a lower voltage across transformer 20, The output from diode 22 becomes less, so that the sum of the output of diodes 2| and 22 becomes relatively more positive. The resulting decrease inthe bias onthe grid of tube 28 causes the tube to draw current and thus produce a voltage drop atedon the grid of tube 30 causes the current through the D. C. winding 8 of reactor |2 to be reduced. This increases the A. C. voltage drop across the primary winding of transformer its new condition. While I have described and illustrated a preferred embodiment of my invention, it will be apparent to those skilled in the art, that many variations and changes may be made therein, without departing from the spirit of the invention or its scope as defined in the appended claims.

I claim:

1.' A method of regulating the temperature of a vacuum tube filament, which consists in induc tivelydetecting a variation in the ratio of filament current with respect to filament voltage,

measuring the value of said variation separately in both voltage and current, and utilizing said.

measured value to provide a reference voltage used to adjust the filament voltage to the value necessary for restoring the filament temperature to normal. I

2. A method of controlling the temperature of a vacuum tube filament, which consists in. 0b taining-an A. C. voltage proportional to the current drawn by the filament, obtaining an A- C. 1

voltage proportional to the voltage across the filament, converting said A. C. voltages into D. C.

voltages, differentially combining said D. 0. voltagesso-as to producea reference voltage, and

utilizing saidv reference voltage to adjust the filathe filament temperv ment :voltage to maintain ature constant.

3. A method of controlling the temperatureof a vacuum tube filament, which consists in deriving a pair of A. C. voltages which are respectively;

proportionalto the current drawn by the filament andrto the voltage across the filament, conj verting said A. C. voltages into D. C. voltages,

v differentially combining said D. C. voltages soas voltage drops to approximately A; of its normal value, or when the current output from tube 38 drops below the lower limit of regulation.

In operation, resistor 25 should be adjusted so that the magnetron filament has the correct.

voltage on it with no plate voltage applied. Tube;

28 is biased at cut-off but nobias isplaced on tube 38 since no voltage drop exists across resistor 29. Tube 38 conducts heavily creating a relatively low A. C. voltage drop across the primary winding of reactor |2 anda relatively high voltage across filament transformer II]. when the intermittentmagnetron plate'voltage is applied, backheating occursand the-filament retoproduce. a reference voltage, amplifying said reference voltage, and utilizing said amplified. voltage to control the filament voltage to main--v tain the filament temperature constant. i

4. In apparatus for regulating the temperature of an electrically heated vacuum tubefilament comp-rising an A. C; power source, a variable impedance element, a vacuum tube filament heating filamenttransformer secondary winding have ingits opposite endsconnected to the ends of said filamentbut otherwise insulated and coupled with a primary winding connected in series with said element-to said power source,;inductive means distinguishing current variations from. voltages.- variations for detecting filament temperature; variations, and means connected with said fie-.1:

tector means for controlling'the impedance of said variable impedance element in response to changes in filament temperature.

5. En apparatus for regulating the temperature of a vacuum tube filament, an A. C. power source, filament transformer means for supplying inductively said filament with current .and voltage from said source, a saturable reactor having a primary winding and a secondary winding, said primary winding being serially connected between said source and said transformer means, means distinguishing current from voltage for deriving a filtered reference voltage which varies in accordance with variations in the temperature of said filament, means for converting said reference voltage into corresponding current variations, and circuit means for [passing said current variations through the secondary winding of said saturable reactor so as to produce corresponding variations in the voltage drop across said primary winding, thereby varying the potential across said transformer means.

6. The invention recited in claim 5 including a plate voltage source, a Vacuum tube, an anode within said vacuum tube, means for connecting said anode with said plate voltage source, and means controlled by the amount of current flowing in said circuit means for disabling said connecting means.

'7. In apparatus for regulating the temperature of a vacuum tube filament, an A. C. source of power, transformer means for supplying the filament with current and voltage from said source of power, saturable reactor means comprising a primary winding and a secondary winding, said primary winding being serially connected between said source of power and said transformer means, means for deriving a pair of A. C. voltages respectively proportional to the voltage and current in said filament, means for rectifying each voltage of said pair to produce two pulsating D. C. output voltages, means for adjusting the relative value of said pulsating D. C. output voltages, means for combining said two pulsating D. C. output voltages to produce a difference voltage output, means for deriving from said difference voltage output an average filtered reference voltage, means for amplifying said reference voltage so as to produce a current which varies in accordance with variations in said reference voltage, circuit means for passing the current produced by said amplifying means through said secondary winding of said reactor means whereby variations in said reference voltage produce corresponding variations in the voltage of said primary winding of said reactor means and consequently in the filament voltage so as to effect corresponding changes in the temperature of said filament.

8. In combination with a magnetron having a filament and an anode, an alternating current circuit supplying inductively heat energy to said filament, a saturable reactor having a pair of alternating current windings connected in parallel in the alternating current circuit and a direct current control winding connected to a direct current power source supplying a direct current circuit coupled inductively with the reactor alternating current windings and wherein the alternatin current windings are responsive to the magnitude of current flow in the direct current winding, an amplifying vacuum tube in the direct current circuit and applying its output to the reactor direct current control winding through a relay operating coil interrupting the voltage to the magnetron anode when the current output of said amplifying vacuum tube becomes outside predetermined limits of regulation, and a detector circuit balanced separately for voltage and current to control the heat energy supplied to the magnetron filament by controlling the bias applied to the amplifying vacuum tube.

KENNETH D. JENKINS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,954,784 Braden Apr. 17, 1934 1,961,703 Morrison June 5, 1934 1,994,976 Kuhle et al Mar. 12, 1935 2,149,080 Wolff Feb. 28, 1939 2,262,044 Philpott Nov. 11, 1941 

